Nanophotonic hot-electron devices for infrared light detection

ABSTRACT

Disclosed are infrared (IR) light detectors. The detectors operate by generating hot electrons in a metallic absorber layer on photon absorption, the electrons being transported through an energy barrier of an insulating layer to a metal or semiconductor conductive layer. The energy barrier is set to bar response to wavelengths longer than a maximum wavelength. Particular embodiments also have a pattern of metallic shapes above the metallic absorber layer that act to increase photon absorption while reflecting photons of short wavelengths; these particular embodiments have a band-pass response.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/606,829, filed Oct. 21, 2019, issuing as U.S. Pat. No. 11,462,656 onOct. 4, 2022, which is a 35 U.S.C. § 371 filing of InternationalApplication No. PCT/US2018/028688, filed Apr. 20, 2018, which claims thebenefit of priority from U.S. Provisional Application No. 62/487,653filed Apr. 20, 2017, which is herein incorporated by reference in itsentirety.

GOVERNMENT RIGHTS

This invention was made with government support under grant no. 1509272awarded by the National Science Foundation. The government has certainrights in the invention.

FIELD

The present document relates to infrared radiation detectors.

BACKGROUND

For this document, infrared light refers to light in the wavelengthrange from 700 nm to 1 mm. IR detectors are widely used intelecommunications, chemical and biological agent detection, smokedetectors, thermal and night vision, and other applications. Currentlythere are two main methods adopted for IR detection. One is sensingchanges in electrical conductivity upon IR illumination, includingphotoconductors. The other is sensing changes in temperature upon IRillumination, including bolometers. The former relies on electron-holepair generation upon optical excitation, while the latter relies on theslight temperature increase by heating associated with absorption of theillumination of different (IR) light.

Photoconductors in the IR regime often suffer from low efficiency andhigh dark current. Bolometers often rely on exotic materials such asV₂O₅, resulting in a high cost and limited application. Furthermore,bolometers tend to have slow response on the order of milliseconds toseconds.

A second category is photoconductors, usually based on photodiodestructures, including semiconductor p-n junction and metal-semiconductorSchottky junction structures. Semiconductor p-n or p-i-n photodiodesrequire that the band gap of the absorbing semiconductor material shouldbe smaller than the photon energy of the IR light. This requirementbecomes increasingly difficult to meet at longer wavelengths as photonenergy is low. Fabrication of such devices often involves elaborateheteroepitaxy. Few long-wavelength devices can be monolithicallyintegrated with silicon electronics read-out circuits, which greatlyincreases the cost and limits their application in large image sensorarrays.

Schottky photodiodes are easy to fabricate because they comprise a layerof metal in contact with a layer of semiconductor. Typically, depositionof metal on a semiconductor is much easier than heteroepitaxy ofsemiconductor photodiodes. The difference between metal work functionand semiconductor work function results in an energy barrier. When IRlight is absorbed in metal, some electrons are excited and gain enoughenergy to overcome the energy barrier and transport to the semiconductorregion, thereby generating electric currents. While Schottky photodiodesare simple to make, their noise is usually high compared tosemiconductor photodiodes because the metal/semiconductor interface isimperfect, leading to dark current generated by interfacial defects thatexceeds the level of regular thermal excitation across the barrier.Responsivity of Schottky photodiodes is lower than that of semiconductorphotodiodes because the metal layer is usually too reflective to absorbIR light efficiently. Additionally, nearly all current IR detectorsystems require exotic compound materials beyond Silicon and usecomplicated read-out circuits.

SUMMARY

Disclosed are infrared (IR) light detectors. The detectors operate bygenerating hot electrons in a metallic absorber layer on photonabsorption, the electrons transported through an energy barrier of aninsulating layer to a metal or semiconductor conductive layer. Theenergy barrier is set to bar response to wavelengths longer than amaximum wavelength. Particular embodiments also have a pattern ofmetallic shapes above the metallic absorber layer that act to increasephoton absorption while reflecting photons of short wavelengths.

In an embodiment, a metal-insulator-conductor infrared photodetectorincludes a metallic infrared light absorber layer configured to generateelectrons with a first kinetic energy upon absorption of photons of theinfrared light. The metallic infrared light absorber layer is disposedover a layer of dielectric material configured to allow passage ofelectrons having the first kinetic energy while blocking electronshaving a second kinetic energy, the dielectric material in turn disposedover a conductive substrate configured to collect electrons passedthrough the dielectric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a MIS(MOS) structure. The Oxide layer is madeof insulating materials such as silicon dioxide, silicon nitride, orsilicon oxynitride, and the semiconductor substrate is made of siliconor other semiconductor or metallic materials. Light is incident from themetal side.

FIG. 2 is a schematic of an MIM device structure with graphene as themetallic absorber. Additional light trapping structure is applied toenhance light absorption in the graphene layer.

FIG. 3 is a graph depicting the electronic band structure of the MISstructure of the present devices. Note the insulator thickness andbarrier height is not to scale.

FIG. 4A illustrates a metallic grating structure designs for enhancinglight absorption near metal/oxide interface incorporating a 2D gratingstructure on top of thin metal film.

FIG. 4B illustrates a metallic grating structure design for enhancinglight absorption near metal/oxide interface incorporating a metal dot orpellet structure on top of thin metal or graphene film, this structureis polarization-independent and mimics the self-assembled Sn nanogratingstructure prepared in experiments.

FIG. 4C illustrates a dual-level metallic grating structure designs forenhancing light absorption near metal/oxide interface on semiconductorsubstrate; this concentrates more incident light will be concentratedtowards metal/insulator interfaces.

FIG. 4D illustrates a dual-level metallic structure for enhancing lightabsorption on semiconductor substrate that combines lithography andself-assembly technique to produce a multispectral absorber with twokinds of feature sizes and periodicity. The larger features (dots withlarger period and size) can be made with lithography and smallerfeatures (dots with smaller period and size) can be made withself-assembly.

FIGS. 5A-5C illustrate a configuration of the nanophotonic structurewith Sn/TiO2/Si, FIG. 5A showing a perspective view of the layout, FIG.5B showing a graph of wavelength versus absorption efficiency. FIG. 5Cillustrates simulated light field distribution indicates the 1550 nmlight is more concentrated near metal/oxide than the 800 nm light,thereby offering some spectral selectivity.

FIGS. 6A and 6B illustrate light trapping structures on single-layergraphene (SLG).

FIG. 7 is scanning electron microscopy images of self-assembledstructures of deposited Sn with varying nominal thickness.

FIG. 8 is a flowchart illustrating a method of manufacture of theMIS/MIM structures herein described.

DETAILED DESCRIPTION OF THE EMBODIMENTS

We seek to provide a new IR sensing solution with a simple, integratedand fully Si CMOS compatible design. Compared to semiconductor IRdetectors, these devices do not require heteroepitaxy of exoticmaterials and allows monolithic integration with Si read outelectronics. Compared to Schottky IR detectors, the interfacial defectsare greatly reduced and IR absorption increased in the metallic layer.

We have developed an IR photodetector structure which only responds tocertain wavelengths range of IR light. This structure provides an IRdetector which can be easily integrated with silicon read-out integratedcircuits. This photodetector is fabricated using silicon/CMOS compatiblematerials and processes.

Our IR photodetector is based on a metal-insulator-semiconductor (MIS)structure or metal-insulator-metal (MIM) structure. The metal layer onthe top of the detector absorbs light and generates excitedphotoelectrons. Kinetic energy of the electrons is dependent on thephoton energy/wavelength of the incident light. The shorter thewavelength, the higher the energy of the photoelectrons. Themetal/insulator interface provides a potential barrier. Only electronsthat have large enough energy can overcome this barrier and reach theelectrode on the other side of the insulator, whether semiconductor ormetal, and generate electrical an output signal. In embodiments, theother side of the insulator is a semiconductor or a metallic substrate.Electrons generated by light with longer wavelengths, which have lessenergy, cannot overcome the energy barrier and thus are blocked by theinsulating layer between metal and substrate. The metal/insulatorinterfacial energy barrier can be adjusted for a targeted IR wavelengthrange.

An embodiment of an IR detector with Metal-insulator-semiconductor (MIS)structure is illustrated in FIG. 1 . The IR detector 100 has a lightabsorber layer 102, an insulating layer 104 and a substrate 106. Forexample, the light absorber can be made of metal (M), the insulatinglayer can be made of insulator (I), and the substrate (S) can besemiconductor (S) or in alternative embodiments metallic materials (M).For simplicity, in this document, this structure can be described as ametal-oxide-semiconductor (MOS) structure. The light absorber is themetal layer, the insulating layer corresponds to the oxide layer and thesubstrate is a semiconductor layer. The materials used in eachpart/layer of these devices are not limited to such choices. Forexample, the metal layer can be metal alloy instead of pure metal, andthe semiconductor substrate can be a silicon or a germanium substrate.

The light absorber metallic layer includes metal or metallic materials.It can be pure metal such as tin (Sn), aluminum (Al) or gold (Au), ormetal alloy such as Aluminum-Copper-Silicon (AuCuSi) alloy Al—Sn, or aconductive silicide such as Nickel Silicide (NiSi), Platinum Silicide(PtSi), or other alloys. Unless graphene is used, the light absorbermetallic layer is between 10 and 100 nanometers thick. The metalliclayer absorbs incident photons and generates electrons with relativehigh excessive energy. The work function of the metallic material, whichis the minimum thermodynamic energy needed to remove an electron fromthe solid material to vacuum outside the solid surface, affects theworking wavelength of the sensor. The sensor receives incoming light 112and operates with an applied voltage 108 and electronic circuitry 110adapted to measure photocurrent in the sensor. Details will be discussedbelow.

Another material usable for this light absorber is a two-dimensionalmaterial such as graphene. Graphene, a monatomic sheet form of carbon(C) is a zero-gap semiconductor with tunable Fermi energy. Previousstudies have shown that graphene and semiconductor can form a Schottkybarrier. Because graphene is metallic at a sufficiently large Fermienergy, in this document it will be referred to as a metallic materialunless otherwise specified. A schematic figure for a graphene-based MIMdevice is shown in FIG. 2 , having metal structures 202 configured tointeract with incoming light 204 and disposed on a graphene layer 206.The graphene layer 206 lies on a thin insulator layer 208. An optionalconductive reflector layer 210 may lie under the insulator layer 208,and is formed on a conductive substrate layer 212. The sensor has anapplied voltage 216 between the substrate layer 212 and the graphenelayer 206, and operates with electronic circuitry 214 configured tomeasure photocurrent in the sensor.

The light absorber metal layer 202, 102, is designed to absorb light(preferably with wavelength between 700 nm and 1 mm) and generatephoton-excited electrons. When photons are absorbed in this layer, someelectrons in the metal layer gain all the energy from the photons. Thusthese electrons have larger kinetic energy than other free electrons inthe metal layer. This process is photon excitation. Kinetic energy ofsuch electrons can be as high as a few eV, according to the energy levelof the incident photons. Since the energy of photon E is related to thewavelength λ in such form:

$E = {h\frac{c}{\lambda}}$

where c is the speed of light and h is Plank constant, we see light withshorter wavelength has greater energy. Thus electrons excited by lightat a shorter wavelength, such as IR light at 1550 nanometers (nm), havegreater energy than those excited by light at longer wavelength, such asIR light at 2000 nm.

To enhance IR light absorption at a wide range of incident angles,nanophotonic structures are built on top of, within or under thismetallic layer. Such structures include but are not limited to gratings402 (FIG. 4A), domes, pyramids, dots/pellets 404 (FIG. 4B), or disks.Each of these structures lies over a full sheet of conductive metal orgraphene 410, an oxide insulator 412, and a semiconductor or metallicsubstrate 414. These structures on top of the metallic layer aretypically from ten nanometers to three hundred nanometers thick. For aparticular embodiment having self-assembled deposited tin (Sn)nanostructures for use at 1550 nm wavelength these structures are 150 nmin thickness. These structures have dimensions close to one wavelengthof the light for which the sensor has peak sensitivity, for aphotosensor having peak sensitivity at 1550 nanometers with round dotstructures, the dot structures should have diameters between 1000 and2000 nanometers and in a particular embodiment 1550 nanometers. For peaksensitivity of 1000 nanometers, the dot structures should havedimensions between 700 and 1300 nanometers. In embodiments the dotstructures have diameters between 50 and 2500 nanometers. For aphotosensor having a grating structure and peak sensitivity of 1550 nm,the grating line pitch should approximately match the wavelength in thegrating material, i.e. the wavelength in the vacuum divided by therefractive index of the grating material. As many embodiments ofphotosensors as herein described are designed for wavelengths between700 and 2000 nanometers wavelength, grating pitches of between 100 and2000 nanometers are appropriate to approximately match thosewavelengths.

In an alternative embodiment, FIG. 4C, in order to concentratephotoelectrons at the interface of oxide insulator 412 and metalabsorber, the metal absorber is formed of a grating on a first 406 andsecond 408 layer. Each grating layer is formed over a finger of oxideinsulator 416, 418, lying over ridges 420 and valleys 422 ofsemiconductor or metallic substrate 414.

In another alternative embodiment, FIG. 4D, in order to absorbphotoelectrons at several specific wavelengths in the IR region, anupper metal absorber layer has self-assembled structures 430 lying ontop of mask-defined structures 432 lying over a full sheet of conductivemetal or graphene 410, an oxide insulator 412, and a semiconductor ormetallic substrate 414.

Such nanostructures can be fabricated in various ways, such aslithography including photolithography and electron beam lithography,lift-off techniques with nanospheres and other templates, such as AnodeAluminum Oxide membranes, and self-assembly.

To optimize the design of the nanophotonic structure, take a figure ofmerit (FOM) as light absorption near the metal/oxide interface. Since“hot” (excited) electrons excited by incident light need to transportthrough the metal, across the oxide insulator, and then towardssemiconductor or metal substrate, it is desirable to reduce the totaldistance and reduce the possibility of inelastic scattering of theseelectrons during the transport process. Previous studies have shown themean free path of hot electrons in noble metal (Au/Ag/Cu) is quite short(a few tens of nm). So we set the FOM as the light absorption within 100nm from metal/oxide interface. Numerical simulations can be used to findan optimized design as shown in FIG. 5A-5B.

In the design 500 of FIG. 5A, a circular discoidal nanostructure 502 oftin overlies a thin tin absorber layer 504, in turn overlying a titaniumdioxide (TiO2) insulator layer 506, in turn overlying a semiconductor ormetallic substrate 508.

To fabricate such nanophotonic structures, both lithography andself-assembly techniques are applied. Lithography, includingphoto-lithography and electron beam lithography provides awell-controlled and precise method for making metallic gratingstructures. For IR application, the metallic gratings have a period near1 um and other feature sizes, including width, and radius, of a fewhundreds of nm. These are achievable by current lithography methods.Another method is to utilize the self-assembled nanostructure ofdeposited metallic materials.

FIGS. 6A and 6B illustrate light trapping structures on single-layergraphene (SLG). FIG. 6A is a cross-section of a light trapping structure600 having Sn (tin) dots 602 on single layer graphene 604, withdielectric materials (Sift) 606 beneath, all overlying a semiconductoror metal substrate 608. FIG. 6B illustrates a light absorption spectrumof SLG with various SiO2 dielectric film thicknesses. While thisrepresentation the dielectric thin film is SiO₂, other dielectricmaterials such as TiO₂, SnO_(x) (1≤x≤2), single layer hexagonal boronnitride (h-BN), and others may function. The metal can be Au, Al, Cu,Ag, silicides, or other metallic materials.

As shown in FIG. 7 , thermally evaporated Sn on Si substrates forms dotswith varying sizes. Fast Fourier transform (FFT) analysis shows that thedots are pseudo-periodic. The average period and size of the dots isdetermined by Sn deposition conditions, such as nominal Sn thickness. Inthis way, a large area of periodic metallic nanostructures can befabricated without the expense of masks and lithography.

Moreover, two types of fabrication techniques can be applied together toform a broad band or multispectral absorber or absorber with a morecontrolled absorbing regime, as shown in FIG. 4 (d). The lithographyhelps prepare larger features and self-assembly adds smaller features.The larger features (structure with larger period and size) can beoptimized for maximum IR absorption and smaller features (structure withsmaller period and size) can be optimized for maximum visible lightreflection or increase the bandwidth of IR absorption by adding anotherresonant peak.

The nanophotonic structures can also be designed for maximum reflectancefor unwanted incident light, such as visible light for IR detector. Theycan be designed to reflect much of incident visible light while maintainrelative high IR absorption. This helps reduce noise and interferencefrom visible light. As shown in FIG. 5B, absorption within 100 nm of themetal/oxide for 1550 nm incident light is ˜48% while the averageabsorption for visible light is about 25%.

Other structures such as a distributed Bragg reflector (DBR) can also beadded to achieve same goal of reflecting much of visible light. Such afilter may include layers of a first and a second transparent materialhaving different refractive indexes, where each layer is approximatelyone-quarter wavelength thick at a particular wavelength for maximumreflection.

The metal layer is also used as one of the electrodes of the detector sothe conductance of metal, both vertical and lateral, is preferably high.

To further increase light absorption within metal layer, a backsidereflector can be added as substrate to reflect the light that istransmitted through the metal-oxide-semiconductor device. Such areflector can be made from metallic materials such as Al, Au, Cu, etc.which have high reflection at IR wavelengths. This configuration workswell in IR region where semiconductor absorption is minimal.

As for graphene and other two-dimensional materials, since they areextremely thin and native light absorption is very low (1-2% for singlelayer), overlying nanophotonic structure is desirable. The FOM of suchstructure is the light absorption of graphene. One exemplary lighttrapping design uses Sn dots and backside reflector, as illustrate inFIG. 6A-6B. The preliminary results indicate that light absorption ofsingle layer graphene can be increased to >40% on a dielectric layer onmetal substrate.

The insulating layer only allows electrons of high kinetic energy topass. Dielectric materials (Sift for example) block electric currentbetween the light absorber layer and the substrate without illumination.However, electrons with high enough kinetic energy cross a very thinlayer of dielectric material without losing any energy by “ballistictransport”. So in this device, those light excited electrons withsufficient energy can cross through such insulating layer while otherelectrons cannot. The oxide material is a material with proper electronaffinity X such that the interfacial barrier height ϕ_(B)=W−X is smallerthan the photon energy of interest, where W is the work function of themetal. It should also have a high breakdown electric field >500 kV/cm.Possible choices of oxide material include SiO₂, AlN, TiO₂, SnO_(x)(1≤x≤2) etc. Another candidate for the insulating layer is a twodimensional material with high band gap, such as hexagonal boron nitride(h-BN). For simplicity, this layer is referenced as “oxide” herein.

The substrate can be a semiconductor material such as Silicon forexample, preferably with low electrical resistance and high electronconcentration. It can also be a metallic material layer on thesubstrate, as the back reflector for better light trapping, a Au layeron silicon or quartz, for example. IR excited electrons which transportthrough insulating layer will reach the substrate and be collected atthe substrate.

The choice of materials for the metal and oxide layers is of crucialimportance. As shown in FIG. 3 , the energy barrier height ϕ_(B) isdetermined by a metal work function W and dielectric layer electronaffinity X.

ϕ_(B) =W−X

Light absorption in the metal layer generates photo-excited electronsand some of them transport towards the oxide layer. If these electronshave kinetic energy greater than ϕ_(B) they will overcome this energybarrier and reach the conduction band of Si on the other side of oxidelayer. Otherwise, the electrons are blocked by the oxide layer. Theinsulating properties of the oxide layer not only eliminate dark currentbut also prevent photoresponse from photons absorbed by semiconductorregion since the oxide layer blocks carriers originating in thesemiconductor.

The thickness of oxide is great enough to prevent electrons with lowenergy transporting to Si via direct tunneling or other process, yet isthin enough to prevent electron energy loss during transport. Forexample, if SiO₂ is used, the proper oxide thickness for such devices isabout 10 nm. Typically the thickness range is between one and fiftynanometers for all oxide insulator layers herein disclosed, unless a 2Dinsulator such as h-BN is used, when thickness may be one-third of ananometer.

The energy barrier height can be adjusted by controlling oxide material.This barrier height determines the threshold wavelength (the longestwavelength that can be detected) of the detector. For example, bychoosing Au for metal layer and SnO₂ for oxide layer, the barrier heightis around 0.9 eV. This is suitable for near IR (NIR) light detectionfrom 780 nm to 1378 nm. Another example is Sn for metal layer and TiO₂for oxide layer. This will gives a barrier height of 0.5 eV, suitablefor IR light with wavelength shorter than 2480 nm, including theimportant telecommunication wavelengths of 1310 nm and 1550 nm. Theinsulating oxide layer significantly reduces the dark current (theelectrical signal that is not generated by target light input), whichcan be optimized by controlling the oxide thickness. They also offer amuch better interface with Si than metal/Si contacts. Compared tometal/semiconductor Schottky junction devices, this device has lessnoise.

A particular embodiment of this MOS configuration uses metal (plasmonicmetal, Sn) as a light absorber, titanium oxide as insulating layer andn-type Si as substrate. The thickness of titanium oxide is about 10 nmand the metal thin film is 100 nm thick. The Si substrate is phosphorusdoped at a level of 1e18 cm⁻³. The thickness of the substrate is about 1um. On top of the metal thin film, periodic metal (Sn) dots are addedfor more light absorption. For working wavelength of 1550 nm, theoptimum period of Sn dots is 1500 nm, the radius of the dots is 450 nmand the height of the dots is 150 nm. Such Sn metal structures can befabricated by photolithography and thermal evaporation using thelift-off technique. This enhances the light absorption within 100 nmfrom Sn/TiO₂ interface up to 48%, 40% higher than a bare 100 nm Sn thinfilm. The potential barrier height is 0.5 eV, blocking response to IRlight with wavelength longer than 2480 nm.

Another exemplary embodiment of this device has single or multiplelayers of graphene as absorber, single or multiple layers of h-BN asdielectric layer and silicon or metal as substrate. Sn dot structure canbe deposited on top of graphene as light trapping structure and metalthin film, such as 100 nm thick Au can be deposited on the backside ofsubstrate as reflector to enhance light absorption within graphene. Thepotential barrier height between graphene and h-BN is 0.5 eV, blockingresponse to IR light with wavelength longer than 2480 nm.

In some embodiments, the devices herein described are formed accordingto the method 800 of FIG. 8 . A conductive layer 608 is deposited 802,in a particular embodiment on a flexible plastic substrate. Atopconductive layer 608 is deposited 804 an insulator layer 606 selectedfrom the insulating oxides herein described, and atop insulator layer606 is deposited 806 a metallic layer 604. Shapes are defined inmetallic layer 604 may be defined by lithography 808, a purpose of suchshapes is to both define absorber structures and a metallic grid forproviding electrical contact to the metallic layer. After thelithography, self-assembled tin dots may be formed 810 atop metalliclayer 604, or an upper metallic layer may be deposited 812. If an uppermetallic layer is deposited 812, small shapes are then formed in thatlayer with lithography 814. Additional metal layers (not shown) may bedeposited and defined with lithography to provide electrical contact tothe metallic layers herein described, and additional insulator layers(not shown) may be deposited to protect and insulate the photosensor.

Combinations:

The photosensors herein described may embody various combinations offeatures, some of which are detailed here.

In an embodiment designated A, a metal-insulator-conductor infraredphotodetector has a metallic infrared light absorber layer of thicknessno more than one hundred nanometers configured to generate electronswith a first kinetic energy upon absorption of photons of the infraredlight; a layer of dielectric material of thickness between one-third andfifty nanometers configured to allow passage of electrons having thefirst kinetic energy while blocking electrons having a second kineticenergy; a conductive layer; wherein the metallic infrared light absorberlayer is disposed on the layer of dielectric material, the layer ofdielectric material being disposed on the conductive layer.

A metal-insulator-conductor infrared photodetector designated AAincludes the embodiment designated A wherein the metallic infrared lightabsorber layer is a metal.

A metal-insulator-conductor infrared photodetector designated ABincludes the embodiment designated A wherein the metallic infrared lightabsorber layer is metal silicide.

A metal-insulator-conductor infrared photodetector designated ACincludes the embodiment designated A wherein the metallic infrared lightabsorber layer is graphene.

A metal-insulator-conductor infrared photodetector designated ADincludes the embodiment designated A, AA, AB, or AC, further including aperiodic or quasi-periodic structures having thickness between ten andthree hundred nanometers disposed on the metallic infrared lightabsorber layer.

A metal-insulator-conductor infrared photodetector designated AEincludes the embodiment designated AD wherein the periodic orquasi-periodic structure comprises a structure selected from the groupconsisting of a grating, dots, and a self-assembled structure.

A metal-insulator-conductor infrared photodetector designated AFincludes the embodiment designated AE wherein the periodic orquasi-periodic structure comprises dots or self-assembled structureshaving typical shape diameters between 50 and 2500 nanometers.

A metal-insulator-conductor infrared photodetector designated AGincludes the embodiment designated AF wherein the dots or self assembledstructures have typical shape diameters between 50 and 2000 nanometers.

A metal-insulator-conductor infrared photodetector designated A4includes the embodiment designated AE wherein the periodic orquasi-periodic structure comprises a grating having pitch between 100and 2000 nanometers.

In a method designated B of fabricating the metallic nanostructure foroptical absorption and photodetection includes depositing a metalliclayer; performing lithography to define shapes having relatively largerfeature sizes and periods; and depositing self-assembled metallicstructures with periods and sizes smaller than the lithography features.

Changes may be made in the above methods and systems without departingfrom the scope hereof. It should thus be noted that the matter containedin the above description and shown in the accompanying drawings shouldbe interpreted as illustrative and not in a limiting sense. Thefollowing claims are intended to cover generic and specific featuresdescribed herein, as well as all statements of the scope of the presentmethod and system, which, as a matter of language, might be said to falltherebetween.

What is claimed is:
 1. A method of detecting infrared light comprising:providing a periodic or quasi-periodic conductive structure comprising agrating having thickness between ten and three hundred nanometersdisposed on a metallic infrared light absorber layer of thickness nomore than one hundred nanometers disposed on a dielectric layer ofthickness between one-third and fifty nanometers and configured to allowpassage of electrons having a first kinetic energy and to blockelectrons of a second kinetic energy, the dielectric layer disposed on aconductive layer; absorbing infrared light of a first wavelength on themetallic shapes, generating, in at least one of the periodic orquasi-periodic conductive structure or the metallic infrared lightabsorber layer, electrons of the first kinetic energy upon absorbing thefirst wavelength of infrared light and electrons of the second kineticenergy upon absorbing light of a second wavelength of infrared light;passing the electrons of the first kinetic energy through the dielectriclayer, the dielectric layer blocking passage of electrons of the secondkinetic energy; and collecting the electrons of the first kinetic energyon the conductive layer.
 2. The method of claim 1 wherein the metallicinfrared light absorber layer comprises a metal.
 3. The method of claim1 wherein the metallic infrared light absorber layer comprises metalsilicide.
 4. The method of claim 1 wherein the metallic infrared lightabsorber layer comprises graphene.
 5. The method of claim 1 wherein theperiodic or quasi-periodic structure further comprises shapes havingtypical shape diameters between 50 and 2500 nanometers.
 6. The method ofclaim 5 wherein the shapes have typical shape diameters between 100 and2000 nanometers.
 7. The method of claim 1 wherein the periodic orquasi-periodic structure comprises a grating having pitch between 100and 2000 nanometers.
 8. The method of claim 7 wherein a periodic orquasi-periodic structure comprising shapes smaller than a pitch of thegrating are provided atop the grating having pitch between 100 and 2000nanometers.
 9. A method of fabricating an infrared detection devicecomprising: forming a conductive collector layer; forming, atop theconductive collector layer, a dielectric layer having thickness betweenone-third and fifty nanometers; forming, atop the dielectric layer, ametallic absorber layer of thickness of no more than one hundrednanometers; and depositing a metallic shape layer of thickness betweenten and three hundred nanometers; performing lithography to defineshapes in the metallic shape layer having relatively larger featuresizes and periods.
 10. The method of claim 9 further comprisingdepositing self-assembled metallic structures with periods and sizessmaller than the shapes defined by lithography.
 11. The method of claim10 wherein the shapes in the metallic shape layer comprise a gratinghaving pitch between 100 and 2000 nanometers.
 12. The method of claim 9wherein the shapes in the metallic shape layer comprise a grating havingpitch between 100 and 2000 nanometers.
 13. The method of claim 9 whereinthe shapes in the metallic shape layer comprise dots having diameterbetween 500 and 2500 nanometers.
 14. The method of claim 13 furthercomprising depositing self-assembled metallic structures with periodsand sizes smaller than the shapes defined by lithography.